Process for making a polyetherester by insertion of a carboxylic acid into a polyether

ABSTRACT

A process for making polyetheresters is disclosed. A polyether is reacted with a carboxylic acid in the presence of a strong protic acid or a metal salt of a strong protic acid to promote insertion of the carboxylic acid into polyether carbon-oxygen bonds to produce a polyetherester. The polyetheresters are useful for various applications in the polyurethane and unsaturated polyester industries.

This is a division of application Ser. No. 08/419,323, filed Apr. 10,1995 now U.S. Pat. No. 5,569,737, which is a division of applicationSer. No. 08/228,845, filed Apr. 18, 1994, now U.S. Pat. No. 5,436,314.

FIELD OF THE INVENTION

The invention relates to a process for making polyetheresters. Inparticular, the invention is a process for preparing polyetherestersfrom polyethers by randomly inserting a carboxylic acid, especially adicarboxylic acid, into the polyether backbone. Polyetheresters areuseful for a wide variety of applications, particularly in theunsaturated polyester and polyurethane industries.

BACKGROUND OF THE INVENTION

Recently, we reported the discovery of a new reaction in which a cyclicanhydride randomly inserts into carbon-oxygen bonds of a polyether togenerate a polymeric composition having both ether and esterfunctionalities (see appl. Ser. No. 07/979,760, now U.S. Pat. No.5,319,006). A Lewis acid such as zinc chloride or zinc bromide catalyzesthe reaction.

When a polyether polyol reacts with a cyclic, saturated anhydride, forexample, the product is a saturated polyetherester polyol useful forpolyurethane applications. Cyclic, unsaturated anhydrides such as maleicanhydride can be used in the process to make unsaturated polyetheresterresins. The unsaturated resins can be reacted with vinyl monomers toproduce cured polyetherester products.

Compared with the synthesis of conventional unsaturated polyesterresins, the process for making polyetheresters by insertion of ananhydride has great flexibility. The average polyether chain lengthbetween ester linkages and the crosslinkability of the polyetheresterare controlled by simply adjusting the proportion of cyclic, unsaturatedanhydride used. Products having a wide range of unsaturation levels areavailable from a single polyether polyol and a single cyclic,unsaturated anhydride.

We also applied the Lewis acid-catalyzed insertion process to thereaction of polyethers and acyclic anhydrides to make glycol diesters(U.S. Pat. No. 5,254,723). Using this process, a relatively crudepolyether polyol mixture can be converted with acetic anhydride to amixture of glycol diacetates. The glycol diacetates are easily purifiedby distillation, and can be used as solvents or chemical intermediates.

The Lewis acid-catalyzed process for anhydride insertion has somedrawbacks. For example, the activity of the catalysts is somewhat lowerthan desirable. Typically, at least about 1 wt. % of the Lewis acidcatalyst is needed for good activity in making the polyetherester.Second, the polyetherester products often have a higher degree of colorthan is desirable. Third, the presence of high levels of residual Lewisacid catalysts in the polyetherester product can have an unfavorableimpact on performance in various end uses. Fourth, a significant amountof volatile by-products are generated in making the polyetheresters. Inaddition, Lewis acids are often not satisfactory for use inmanufacturing operations because they tend to attack reactors and otherprocessing equipment.

A key limitation of the Lewis acid-catalyzed insertion process formaking polyetheresters is that the reaction does not appear to work forcarboxylic acids. As a practical matter, the cost and availability ofvarious cyclic anhydrides limit the kinds of polyetherester productsthat can be made.

Because of the wide range of available dicarboxylic acids, and therelatively low cost of most dicarboxylic acids relative to thecorresponding anhydrides, a process that would enable insertion ofdicarboxylic acids into polyethers to give polyetheresters would bevaluable. A preferred process could use aliphatic and aromaticdicarboxylic acids commonly used for making polyester resins, such asisophthalic acid, adipic acid, and the like. A preferred process wouldavoid some of the other disadvantages of the Lewis acid-catalyzedprocess for making polyetheresters by anhyddde insertion, such as thegeneration of volatile by-products. Ideally, the process would givelow-color polyetheresters useful for a variety of products, includingunsaturated polyesters and polyurethanes.

SUMMARY OF THE INVENTION

The invention is a process for making polyetheresters from polyethers.The process comprises reacting a polyether with a carboxylic acid in thepresence of a strong protic acid or a metal salt of a strong protic acidin an amount effective to promote insertion of the carboxylic acid intocarbon-oxygen bonds of the polyether to produce the polyetherester.Protic acids useful in the invention have a pKa less than about 0. Themetal salts are derived from these protic acids.

We surprisingly found that insertion of carboxylic acids into polyethersto give polyetheresters, which apparently does not occur with Lewisacids, proceeds smoothly in the presence of a strong protic acid (pKaless than about 0) or a metal salt of a strong protic acid. The processof the invention avoids some of the problems of the Lewis acid-catalyzedanhydride-insertion process. Low catalyst levels suffice, ordinaryreactors and equipment can be used, generation of volatile by-productsis minimized, and low-color, high-quality polyetheresters result.

A wide variety of aliphatic and aromatic carboxylic acids can be used inthe process of the invention. The ability to insert carboxylic acids,especially dicarboxylic acids, into a polyether enables the preparationof a broad array of polyetheresters, and greatly expands the utility ofthe insertion reaction. Because the reaction works with simple, readilyavailable dicarboxylic acids such as isophthalic acid and adipic acid,the process of the invention is an economical, general route topolyetheresters. Polyetheresters made by the process of the inventionare useful in a variety of applications, particularly in the unsaturatedpolyester and polyurethane industries.

DETAILED DESCRIPTION OF THE INVENTION

In the process of the invention, a polyether reacts with a carboxylicacid in the presence of a strong protic acid or a metal salt of a strongprotic acid in an amount effective to promote insertion of thecarboxylic acid into carbon-oxygen bonds of the polyether to produce apolyetherester.

Polyethers suitable for use in the invention are those derived from baseor acid-catalyzed ring-opening polymerization of cyclic ethers such asepoxides, oxetanes, oxolanes, and the like. The polyethers have repeatunits of oxyalkylene groups (--O--A--) in which A has from 2 to 10carbon atoms, preferably from 2 to 4 carbon atoms. The polyethers canhave different end groups, depending upon how the polyethers are made ormodified. For example, the polyether can have hydroxyl, ester, ether,acid, olefinic, or amino end groups, or the like, or combinations ofthese. Mixtures of different types of polyethers can be used.

Preferred polyethers for the process of the invention am polyetherpolyols. Suitable polyether polyols include, for example,polyoxypropylene polyols, polyoxyethylene polyols, ethyleneoxide-propylene oxide copolymers, polytetramethylene ether glycols,oxetane polyols, and copolymers of tetrahydrofuran and epoxides.Typically, these polyols will have average hydroxyl functionalities fromabout 2 to about 8, and number average molecular weights from about 250to about 25,000. The polyether polyols can be recycled polyols derivedfrom a polyurethane foam, elastomer, sealant, or the like.

A carboxylic acid is used in the process of the invention. Usefulcarboxylic acids include mono-, di-, and polycarboxylic acids. Thecarboxylic acid can be saturated or unsaturated. Dicarboxylic acids aregenerally preferred. Particularly preferred are linear, branched, andcyclic C₃ -C₄₀ aliphatic dicarboxylic acids and C₈ -C₄₀ aromaticdicarboxylic acids.

Suitable carboxylic acids for use in the invention include, for example,acetic acid, propionic acid, decanoic acid, benzoic acid, steadc acid,linoleic acid, oleic acid, adipic acid, suberic acid, malonic acid,succinic acid, glutaric acid, pimelic acid, itaconic acid, suberic acid,azelaic acid, sebacic acid, maleic acid, fumaric acid, citraconic acid,phthalic acid, isophthalic acid, terephthalic acid, dimer acids,tetrahydrophthalic acid, halogenated phthalic and tetrahydrophthalicacids, and the like. Preferred carboxylic acids are adipic acid, maleicacid, fumaric acid, phthalic acid, and isophthalic acid.

In one embodiment of the invention, the carboxylic acid is generated insitu by using, instead of the carboxylic acid, an anhydride and at leastabout one molar equivalent of water. For example, maleic anhydride,water, catalyst, and polyol can be combined and heated at a relativelymild temperature that is effective to cause hydrolysis of the anhydride(40°-60° C.) to produce maleic acid. The reaction temperature of themixture is then elevated to promote insertion of the diacid into thepolyether to generate a polyetherester product. See Example 4 below.

A strong protic acid catalyzes the process of the invention. Suitableprotic acids are inorganic and organic protic acids that have a pKa lessthan about 0. Generally, the acids will be stronger than organiccarboxylic acids. Suitable acids include arylsulfonic acids,alkylsulfonic acids, and halogenated alkyl- and arylsulfonic acids. Alsosuitable are hydrogen halides, halosulfonic acids, tetrafluoroboricacid, heteropolyacids, and sulfuric acid. Mixtures of different acidscan be used. Examples of suitable acids include, but are not limited to,p-toluenesulfonic acid, trifluoromethanesulfonic acid (triflic acid),trichioromethanesulfonic acid, hydrochloric acid, hydrobromic acid,hydriodic acid, tetrafluoroboric acid, sulfuric acid, phosphotungsticacid, phosphomolybdic acid, and the like. Preferred protic acids aresulfuric acid, p-toluenesulfonic acid, and phosphotungstic acid.

The protic acid is used in an amount effective to promote randominsertion of the carboxylic acid into polyether carbon-oxygen bonds andproduce a polyetherester. The preferred amount to be used depends onmany factors, including the desired reaction rate, the type of polyetherand carboxylic acid used, catalyst type, reaction temperature, and otherconsiderations. If the catalyst is omitted, carboxylic acid insertiondoes not occur; with too little catalyst, the insertion reaction isslower than desirable. Generally, it is preferred to use an amount ofprotic acid within the range of about 0.01 to about 1 weight percentbased on the amount of polyether used. A more preferred range is fromabout 0.05 to about 0.5 weight percent.

We also found that metal salts of strong protic acids are effectivecatalysts for the process of the invention. The metal salts are derivedfrom protic acids that have a pKa less than about 0. Thus, the saltsuseful in the invention are generally derived from the protic acidsdescribed above as suitable for use in the process. Mixtures of strongprotic acids and metal salts of the acids can be used.

Preferred metal salts useful as catalysts for the process of theinvention are metal salts of arylsulfonic acids, aikyisulfonic acids,halogenated aryl- and alkylsulfonic acids, tetrafluoroboric acid,sulfuric acid, heteropolyacids, and halosuifonic acids. Sulfonic acidsalts, especially triflate salts, are particularly preferred.

Preferred metal salts include metal salts of strong protic acids (pKaless than about 0) in which the metal is selected from Group IA, GroupIIA, Group lIB, Group IB, Group IIIA, Group IVA, Group VA, and GroupVIII. Thus, the metal can be, for example, lithium, potassium,magnesium, zinc, copper, aluminum, tin, antimony, iron, nickel.

Suitable metal salts include, but are not limited to, lithium triflate,sodium triflate, magnesium triflate, zinc triflate, copper(II) triflate,zinc tetrafluoroborate, zinc p-toluenesulfonate, aluminum triflate,silver tetrafluoroborate, iron(II) tetrafluoroborate, nickel(II)tetrafluoroborate, tin(II) triflate, and the like. Mixtures of metalsalts can be used.

The metal salt is used in an amount effective to promote randominsertion of the carboxylic acid into polyether carbon-oxygen bonds andproduce a polyetherester. As with the protic acid catalysts, thepreferred amount to be used depends on many factors, including thedesired reaction rate, the type of polyether and carboxylic acid used,catalyst type, reaction temperature, and other factors. Generally, it ispreferred to use an amount of metal salt within the range of about 1part per million (10⁻⁴ wt. %) to about 1 weight percent based on theamount of polyether used. A more preferred range is from about 10 partsper million to about 0.5 weight percent.

An anhydride is optionally included in the process of the invention. Theanhydride can be cyclic or acyclic, saturated or unsaturated. In a"cyclic" anhydride, the anhydride functionality is contained within aring, such as in phthalic anhyddde and maleic anhyddde. "Acyclic"anhydddes, which include acetic anhydride, propionic anhydride, and thelike, have no such ring. "Saturated" anhydrides contain no ethylenicunsaturation, although they may contain aromatic rings. Phthalicanhydride, propionic anhydride, and succinic anhydride are examples ofsaturated anhydrides. "Unsaturated" anhydrides contain ethylenicunsaturation. This unsaturation becomes incorporated into thepolyetherester, and can be used for crosslinking. Examples includemaleic anhydride, itaconic anhydride, and the like.

Specific examples of suitable anhydrides for use in the inventioninclude, but are not limited to, acetic anhydride, propionic anhydride,maleic anhydride, phthalic anhydride, succinic anhydride,tetrahydrophthalic anhydride, citraconic anhydride, itaconic anhyddde,and aryl-, alkyl- and halogen-substituted derivatives of these. Mixturesof anhydddes can be used. Where unsaturated polyetheresters are desired,maleic anhydride or mixtures of maleic anhydride and phthalic anhydrideare particularly preferred.

The process of the invention is conveniently performed by combining thepolyether, carboxylic acid, and catalyst in any desired order or manner,and heating the mixture at the desired reaction temperature underconditions effective to promote carboxylic acid insertion to produce apolyetherester. The progress of the reaction can be followed bymeasuring the acid number, which will decrease and level off as thereaction proceeds. The process can be performed batchwise,semi-batchwise, or continuously as desired.

Polyetherester products obtained from the process of the inventioncommonly have a large proportion of carboxylic acid end groups. It isgenerally preferred to heat the polyetherester product with a glycolsuch a propylene glycol, ethylene glycol, dipropylene glycol, or thelike, to esterify these acid groups with the glycol. The resultingpolyetheresters have hydroxyl end groups and lower acid numbers.Compositions with low acid numbers are often needed for use in certainapplications, such as, for example, formulation into polyurethanesealants and elastomers.

The amount of glycol used is preferably at least about 1 equivalent ofglycol for each residual carboxylic acid end group. Typically, thisamounts to heating the polyetherester with at least about 5-10 wt. % ofthe glycol. The glycol is typically heated with the polyetherester atabout the same temperature as that used for the insertion reaction untilthe acid number of the mixture drops to the desired level. Any excessglycol is removed by stripping. A thermosettable unsaturatedpolyetherester resin might be made, for example, by reacting a polyetherpolyoi and 30 wt. % maleic acid to give a polyetherester product havingan acid number in the 100 to 200 mg KOH/g range, then heating theproduct with 10 wt. % propylene glycol to produce a new polyetheresterhaving an acid number within the range of about 30 to about 80 mg KOH/g.

Any convenient reaction temperature can be chosen for makingpolyetheresters by the process of the invention provided that thetemperature is sufficient to promote insertion of the carboxylic acidinto the polyether. Generally, however the reaction is too slow to bepractical at temperatures below about 60° C. Preferably, the process isperformed at a temperature within the range of about 80° C. to about250° C. A more preferred range is from about 100° C. to about 220° C.;most preferred is the range from about 150° C. to about 200° C.

It is preferred, although not necessary, to perform the process under aninert atmosphere of nitrogen, argon, or the like. Preferably, thereaction mixture is well agitated during the carboxylic acid-insertionprocess. Reactions are typically complete within 5-12 h.

The catalyst is optionally removed from the polyetherester productbefore using it in a polyurethane or polyester application. Catalystremoval, although not usually required, may be desirable for certainend-uses that are particularly sensitive to the presence of residualacids or salts. Any suitable method generally known in the art forremoving acids or salts from polyethers and polyester resins can beused. Salts can often be removed by ordinary filtration or adsorption.Acidic catalysts can be removed, for example, using a basic ion-exchangeresin, water washing, adsorption onto basic alumina or magnesiumsilicate, or by converting the acid to a salt and filtering to removethe salt.

The process of the invention offers significant advantages over earlierprocesses for making polyetheresters, particularly the Lewisacid-catalyzed anhydride-insertion process. The ability to usedicarboxylic acids is valuable because the corresponding anhydrides areoften not available or, if available, are more costly than thedicarboxylic acids. Because dicarboxylic acids can be used, theinvention enables the preparation of a broad spectrum ofpolyetheresters, and greatly expands the utility of the insertionreaction for making polyetheresters.

The process avoids some drawbacks of Lewis acid-catalyzed anhydrideinsertions. Volatile by-products generated in that process, includingminor amounts of aldehydes and cyclic ethers, are minimized or are notgenerated in the process of the invention. In addition, the process ofthe invention gives polyetheresters that are low in color, often animportant asset for polymers intended for use in coatings or sealants.

A wide variety of polyetherester products can be made, depending on thetype of carboxylic acid(s) used, the relative proportion of unsaturatedto saturated carboxylic acid, the relative proportion of carboxylic acidto polyether, the nature and molecular weight of the polyethercomponent, the relative amount of any anhydride optionally used, andother factors.

An unsaturated polyetherester resin can be made by reacting thepolyether with at least some proportion of an unsaturated carboxylicacid, preferably an unsaturated dicarboxylic acid, or by including acyclic, unsaturated anhydride such as maleic anhydride in the process.The unsaturated polyetherester resin can be used like conventionalunsaturated polyester resins. For example, the polyetherester resin canbe combined with a vinyl monomer such as styrene, and heated in thepresence of a free-radical initiator to produce a cured polyetheresterproduct.

Saturated and unsaturated polyetheresters made by the process of theinvention from polyethers and di- or polycarboxylic acids will beuseful, for example, in polyurethane foams, elastomers, sealants, oradhesives, as replacements for polyether or polyester polyols.

Polyetherester products derived from reaction of a polyether and amonocarboxylic acid will generally have different uses. Polyethershaving one or more ester end groups will generally result from reactionof polyethers with monocarboxylic acids. The products will have lowermolecular weights than the starting polyether because chain scissionresults from insertion of a mono-carboxylic acid. Because the insertionoccurs at random places in the polyether chain, the products will alsohave broad molecular weight distributions. These products should haveutility in such specialized applications as functional fluids anddrilling muds, as well as in vadous polyurethane and unsaturatedpolyester applications. The process of the invention can be tailored togive products having the desired functionalities and properties.

The following examples merely illustrate the invention. Those skilled inthe art will recognize many variations that are within the spidt of theinvention and scope of the claims.

EXAMPLE 1.

PreDaration of a Polyetherester from Polypropylene Glycol and AdipicAcid using p-Toluenesulfonic Acid as a Catalyst

A one-liter reaction kettle is charged with a polypropylene glycol(about 2000 mol. wt., 500 g), adipic acid (125 g), and p-toluenesulfonicacid (6.25 g). The mixture is heated to 185° C. After 4 h, the acidnumber drops to 40 mg KOH/g. Propylene glycol (294 g) is added, andheating continues for another 4 h until the acid number is less than 2.Excess propylene glycol is removed by stripping, and a light yellowpolyetherester product (607 g) is obtained. GPC results: Mn=1975;Mw/Mn=1.65.

EXAMPLE 2. Preparation of a Polyetherester from Polypropylene Glycol andIsophthalic Acid using p-Toluenesulfonic Acid as a Catalyst

Isophthalic acid (64 g), polypropylene glycol (about 2000 mol. wt., 255g), and p-toluenesulfonic acid (3.2 g) are heated for 11 h at 185° C. toproduce a mixture that has an acid number of 50 mg KOH/g. Propyleneglycol (158 g) is added, and heating continues for another 3 h to lowerthe acid number to less than 2. Excess propylene glycol is removed bystripping, and a yellow polyetherester product (315 g) is obtained.

EXAMPLE 3. Preparation of a Polyetherester from Polypropylene Glycol andAdipic Acid using Zinc Triflate as a Catalyst

The method of Example 1 is followed, but zinc triflate (0.31 g) is usedinstead of p-toluenesulfonic acid as a catalyst. After heating for 5.5 hat 185° C., the acid number is 51 mg KOH/g. Propylene glycol (300 g) isadded, and heating continues for 10 h to lower the acid number to lessthan 2. Excess propylene glycol is stripped to give 530 g of lightyellow polyetherester product.

EXAMPLE 4. Preparation of a Polyetherester from Polypropylene Glycol andMaleic Acid using D-Toluenesulfonic Acid as a Catalyst In-situGeneration of Maleic Acid from Maleic Anhydride and Water

A two-liter resin kettle equipped with a mechanical stirrer, nitrogensparge tube, thermocouple, and distillation head is charged with apolyether triol (3000 mol. wt., alI-PO triol, 975 g), maleic anhydride(525 g), and p-toluenesulfonic acid (1.5 g). The mixture is heated toabout 55° C. until a homogeneous solution results. Water (152 g) is thenadded, and the mixture is stirred until the exotherm from the hydrolysisreaction of maleic anhydride and water dissipates. The temperature ofthe mixture is then gradually increased to 185° C. and is held at thattemperature until the acid number drops to 138 mg KOH/g. Propyleneglycol (243 g) is added, and heating continues until the acid numberfalls to 53. After vacuum stripping, a clear, nearly water-white resinresults.

The resin is blended with styrene (60 wt. % resin). In the SPI 180° F.gel time test (Society of the Plastics Industry, Resin TechnicalCommittee Test Procedure, published 1986), the resin shows a peakexotherm of 425° F. at 5 minutes, 40 seconds. The resin can be curedwith cobalt naphthenate and methyl ethyl ketone peroxide or a mixture ofbenzoyl peroxide and tert-butyl perbenzoate to produce a clear, hardplastic article.

EXAMPLE 5. Preparation of a Polyetherester by Insertion of IsophthalicAcid and Maleic Anhydride

A one-liter resin kettle is charged with the same polyether triol usedin Example 4 (400 g), isophthalic acid (133 g), and p-toluenesuifonicacid (6.7 g). The mixture is heated to 185° C. for 12 h to lower theacid number to 100 mg KOH/g. Maleic anhydride (133 g) is then added, andheating continues for 4 h, after which the acid number is 113. Propyleneglycol (52 g) is added, and the mixture is heated to 185° C. to reducethe acid number to 66. The mixture is vacuum stripped to give a clear,yellow resin. The resin can be blended with styrene and cured aspreviously described to give a clear, hard plastic article.

EXAMPLE 6. Preparation of a Low-Viscosity Polyether Diester Fluid from aPolyether Polyol and Coconut Fatty Acid

A one-liter reactor is charged with 300 g of a polyoxypropylene triol(3000 mol. wt., viscosity=500 cps), 350 g of coconut fatty acid (amixture of monocarboxylic acids, ave. mol. wt.=214), and 8.6 g ofp-toluenesulfonic acid. The mixture is heated at 195° C. for 14 h untilthe acid number is 12 mg KOH/g. Dipropylene glycol (15 g) is added, andthe mixture is heated for another hour to give 650 g of a polyetheresterproduct. The product is diluted with toluene, and is washed with aqueoussodium bicarbonate solution. Toluene is removed under vacuum to give aliquid product having an acid number <2 mg KOH/g, and an average mol.wt. of about 800. The average polyether chain has about 7 oxypropyleneunits. The viscosity of the product is about 33 cps at room temperature,and about 17 cps at 40° C.

The preceding examples are meant as illustrations. The following claimsdefine the scope of the invention.

We claim:
 1. A process for making a cured polyetherester product, saidprocess comprising:(a) reacting polyether with an unsaturateddicarboxylic acid in the presence of a protic acid having a pKa lessthan about 0 in an amount effective to promote random insertion of thedicarboxylic acid into polyether carbon-oxygen bonds and produce anunsaturated polyetherester resin; (b) combining the unsaturatedpolyetherester resin with a vinyl monomer and a free-radical initiator;and (c) heating the mixture at a temperature effective to produce thecured polyetherester product.
 2. A process for making a curedpolyetherester product, said process comprising:(a) reacting a polyetherwith an unsaturated dicarboxylic acid in the presence of a metal salt ofa protic acid, wherein the protic acid has a pKa less than about 0, inan amount effective to promote random insertion of the dicarboxylic acidinto polyether carbon-oxygen bonds and produce an unsaturatedpolyetherester resin; (b) combining the unsaturated polyetherester resinwith a vinyl monomer and a free-radical initiator; and (c) heating themixture at a temperature effective to produce the cured polyetheresterproduct.
 3. A cured polyetherester product made by the process ofclaim
 1. 4. A cured polyetherester product made by the process of claim2.